You use surrogate to describe a person or thing that is given a particular role because the person or thing that should have the role is not available. 替代的
adjective [原级]替代的,代理的
Martin had become Howard Cosell's surrogate son. 马丁已成为霍华德马考塞尔的代子了。
He found a psychotherapist near him to supervise his work with a surrogate, and flew the surrogate there from Los Angeles. 他发现一名心理治疗师和一名代理在他旁边监督他的工作,并让代理从洛杉矶飞往那里。